The present invention relates to optical sensors applicable as a motion sensor to distinguish between different types of motion, without regard to orientation of the sensor, and applicable as an angular position sensor to determine angular position in two degrees of freedom.
Motion sensors are used in Personal Alert Safety Systems (PASS) which are worn by personnel that work in isolated and dangerous environments such as, for example, firemen, industrial workers, chemical workers or security guards. Such PASS devices monitor, among other things, the movement of the person, and provide an alarm or other indication when sensed movement is determined to be abnormal, indicating incapacity of the person. Prior PASS devices incorporate various types of motion detectors for this purpose.
A first type of motion detector is found in U.S. Pat. No. 4,978,946, issued Dec. 18, 1990, and comprises an electrically conductive enclosure including a conductive circuit and containing a conductive ball. Motion is detected when the ball makes contact to both the conductive enclosure and the conductive circuit.
Another type of detector is presented in German Offenlegungsschrift 28 48 747, published May 5, 1980, which includes a rotatable member having a peripheral surface with differing reflective characteristics. Light, reflected from the periphery of the rotatable member, is detected to evaluate motion.
U.S. Pat. No. 4,450,353, issued May 22, 1984, presents an optical tilt detector which includes a chamber containing a ball in damping liquid, a bottom surface of the chamber being pyramidal. Tilting of the device is detected when the ball is displaced from an axis of the device, allowing light to strike a light detector located on the axis. The direction of tilt relative to the axis cannot be detected.
A problem with prior PASS devices has been the incidence of false alarms when a wearer is moving only slightly. Such slight movements are often erroneously detected as worker incapacity, and a false alarm is sounded. The occurrence of such false alarms may actually encourage a worker to deactivate the PASS device, a potentially dangerous situation. Another problem has been sensor orientation sensitivity. Often, a sensor will lose its ability to detect motion when inverted, or when located at an angle.
In addition, other applications, such as in the toy, automobile or aerospace industries, or other industrial applications such as robotic assembly, may have need for a motion sensor which is capable of distinguishing between various types of motion, despite the orientation of the sensor.